looking for feedback about brakes...

i'm definitely doing disc conversion up front. the question is (or questions are), should i do discs in the rear, too? may swap an exploder 8.8 in the rear in which case i'd grab one with discs.

or, keep drums in the rear and spring for a booster in addition to the new dual master cylinder (which i'd get either way).

that reminds me, different MC depending on whether drum/disc in the rear, right? any recommendations for these (looks like all the usual suspects carry them).

thanks!

 

Are you planning to keep the master cylinder under the floor?

I personally would just do disc up front unless they come with the rear axle, and I would definitely do power brakes.

Are you keeping the original front axle and just adding a disc kit?

 

Yes.
Same price at junkyard either way, so am leaning toward disc (if I end up with 8.8 that is).
Yes.

I think I've seen a kit offered somewhere that includes power booster and dual MC (plus adapter) that still mounts underneath... though not sure how the E4OD will mount up to that x-member or something else in its place.

Wonder how much of a hassle it would be to add power booster later, to keep initial costs down?

 

Since you have no preference, maybe look into maintenance cost? The disc rear may have an internal mini drum for parking brake? cost of rotors and pads vs shoes and drums?

I don't know how much you would save vs hassle to install and extra parts later?

 

Doesn't matter to the master cylinder if it is discs or drums. But you probably want a proportioning valve if you often drive it empty or you'll lock up the rear too easy especially with servo assistance.

 

I believe there is a difference to the master cylinder, bore sizes will be different, given the fluid requirements for disc v drums is very different.

 

It can matter to the master cylinder as they make some masters with two different sized pistons. The bigger piston being for the disc and smaller for drums.

 

I went with disks on all four corners. I used Cadillac Eldorado rear calipers that have parking brakes. Speedway up front, 2psi residual valves front and rear, manual proportion valve in the rear and power booster under floor boards with Corvette master cylinder. It stops

 

FYI If you put the manual master cylinder in first and then add the vacuum boost later you'll have to re do your brake lines and possibly even your wiring to the brake light switch.

Discs all the way around are nice but drums in the back will get the job done. Heck they had drums for years even on COP cars that stopped vehicles with a lot more weight than our old trucks.

SOME master cylinders have check valves installed and won't need residual check valves. Probably best to call the vendor and talk to them.

 

If anything, I would only do front disk brakes. Rear disk brakes are mainly to say you have rear disk brakes. Plus I haven't seen rear disk brake conversions for any car or truck that didn't have kind of a "rigged" emergency brake setup.


As far as vacuum power assist for the brakes. Be certain whatever engine you are using will develop 12" or more vacuum at idle. Less than that and the power assist suffers. Performance engines don't work well with vacuum assist power brakes. Manual brakes take less pedal effort than poor operating power assist brakes. You'll need a master cylinder for rear drum/front disk brakes. The rear drum outlet has a residual check valve in it. Also the reservoir for the disk portion is larger than the reservoir for the drum portion. On some cars the pistons inside the master cylinder are also different sizes (but I don't think for your application).


On mine, I will do the dual reservoir conversion and not the power assist. I've had cars with poor operating power assist brakes and I don't want that again. The power assist puts some limitations on the motor build.

 

I think you can add a vacuum reservoir if you need to store some, and even a vacuum pump to charge one depending on your engines vacuum capabilities, or just go hydraulic booster, or electric if they have them yet?

 

I don't know if vacuum reservoirs help much. My thinking is its not only the volume available but also the pressure (vacuum) available. If you are idling through a parking lot or slow stop and go through town a reservoir might not work so well. I've only come across one person that tried one, it was on a 1969 Z28, he said no it didn't help much at all. Switched it out for an electric vacuum pump which helped. The only down side is the electric pump ran a lot to supply sufficient vacuum. I've had a couple of cars make only 9 to 12 inches of vacuum at idle. At 12 it's okay. Less than that and the power assist worked sporadically.


If somebody offered a hydro boost power assist, then that would definitely work around the low vacuum source problem.

 

I went with power and disc's all the way around and I am very happy with that decision. I need to finish up the emergency brake piece but I really like the confidence that goes along with stopping predictably and in a straight line. Mine is a mustang II in the front and explorer rear end.

 

With disk brakes the power booster is a must-have. I went manual with disk/drum. That is the next thing on my to-do list....add a power booster. I have the 11-5/8 disks up front....disks still take more pedal force than a drum brake setup.

BTW...Chuck is spot on...residual pressure valves on the disks keep the pads close to the disk & minimize pedal travel without causing drag. A proportioning valve will allow you to balance the braking front to back. Residual pressure valves on the drum brake part of your system will prevent the shoes from releasing so fast that the wheel cylinders suck in air when you let off the brakes.

Dan

 

Disc brakes do not always require servo assistance. If you've just nailed on discs using the original master cylinder, then I suspect your bore ratio from master to caliper are wrong. Do you know the master cylinder bore versus the bore of the caliper pistons? Pedal ratio comes into it. I have had several sports cars with non assisted brakes, and they have had some of the most powerful( and best feel) of any brakes I've used.
Your info on the residual valve purpose isn't accurate.